The present invention relates to medical devices (e.g., implantable pulse generators) that include a polymer and a polynucleotide. Preferably, the medical device can be used to prevent or treat medical device-associated infections. In some aspects of the present invention, the medical devices carry a polynucleotide that encodes an antimicrobial peptide and inhibits the growth of pathogens. In other aspects of the present invention, the medical devices carry eukaryotic cells (e.g., endothelial cells) that express an antimicrobial peptide and inhibit the growth of pathogens.
The insertion of implants has become a widely accepted and often life-saving procedure. The past few years have seen a dramatic increase in the variety and numbers of medical devices. It is estimated that currently world-wide there are some 6,000 distinct types or generic groups of medical devices, and some 750,000 or more brands and models, ranging from very simple devices to very complex systems. A study in 1989 estimated that world-wide approximately 1,000,000 implants are performed annually; the number of additionally used catheters for diagnostic and therapeutic means exceeds this number considerably.
Infection is the most feared, if not the most serious complication of the numerous devices and materials inserted. Treatment of such infections is difficult and most often infection is irreversible, requiring in many cases complete removal of the catheter or implant. Technological refinements in materials and design and increasing surgical experience generally lowers the incidence of infectious complications; however, infection remains a constant cause of morbidity and mortality.
The impact and clinical importance of implant-related infections may be more appreciated considering several factors. One important factor is the millions of patients in whom prostheses of one sort or another are present. Another important factor is the severity of illness that results from device-related infections. In most instances, infection involving a totally implanted device results in function-loss and the need for surgical removal in order to achieve a cure. Depending on the device type, e.g., with prosthetic heart valves or vascular grafts, mortality is high following infection. A third factor is the economic consequences that are measured in the costs of making the diagnosis and in treating a device-related infection. It is estimated that the costs of treating an infected joint prosthesis exceed four- to sixfold the costs of the original prosthetic joint replacement.
Approaches to reduce device-related infections initially were focused on improvements of the surgical technique, including modification of the operating room area and the use of prophylactic antibiotics at the time of surgery. Despite the introduction of these meticulous aseptic measures the occurrence of device-related infections could not be completely eliminated.
An alternative approach is to focus on the implant itself, and consequently on modification of the device to enhance infection-resistance by providing surfaces on the device that promote appropriate integration of the surrounding tissue(s) with the device surface. The underlying concept is that encouraging rapid colonization and integration of the device surface with tissue cells protects the implant surface from bacterial colonization.
A considerable amount of attention and study has been directed toward preventing colonization of bacterial and fungal organisms on the surfaces of orthopedic implants by the use of antimicrobial agents, such as antibiotics, bound to the surface of the materials employed in such devices. The objective of such attempts has been to produce a sufficient bacteriostatic or bactericidal action to prevent colonization. Practice of the prior art coating methods results in an orthopedic implant or medical device wherein the effectiveness of the coating can diminish over time. After insertion of the medical device or orthopedic implant, the antibiotics can leach from the surface of the device into the surrounding environment. Moreover, bacterial pathogens have become increasingly resistant to commonly used antibiotics. In some cases, there are no remaining first-line options for therapy. A recently published trend analysis on bacterial pathogens isolated from blood in England and Wales from 1990 to 1998 showed an upward trend in total numbers of reports of bacteraemia. The five most cited organisms accounted for over 60% of reports each year. There was a substantial increase in the proportion of reports of Staphylococcus aureus resistant to methicillin, Streptococcus pneumoniae resistance to penicillin and erythromycin, and Enterococcus faecalis and Enterococcus faecium resistance to vancomycin.
Antimicrobial peptides are a type of antibiotic. The first antimicrobial peptides were identified in 1939 by Dubos who demonstrated that xe2x80x98an unidentified soil bacillusxe2x80x99 produced antibacterial compounds that could prevent pneumococcal infections in mice (Boman et al., xe2x80x9cAntimicrobial Peptides,xe2x80x9d Ciba Foundation Symposium, John Wiley and Sons, Chicester (1994)). In the 1960s, a bee venom toxin and a peptide in frog skin were claimed to be antibacterial. Since then, antimicrobial peptides have been isolated from insects (cecropins from the moth Hyalophora cecropia and Drosophila melanogaster, insect defensins from the fleshflies Phormia terranovae and Sacrophaga peregrina), from the skin of the African clawed frog Xenopus laevis (magainins), from the horse shoe crab (tachyplesins), and mammalian granulocytes (defensins), macrophages (murine microbicidal proteins), and platelets (thrombocidins). Their widespread distribution is remarkable and makes it highly likely that these components play an important protective role as a first line of defense against infections. Although antimicrobial peptides vary considerably in length, almost all of them are of cationic nature.
In humans, numerous antimicrobial peptides have been isolated and characterized from multiple sources, including neutrophils (also referred to in the art as polymorphonuclear leukocytes), T cells, bronchoalveolar lavage, platelets, plasma, wound fluid, and various organs. Furthermore, over the past few years a range of antimicrobial peptides have been found in epithelial tissue of airways, urogenital tissue, skin, and intestine. These findings suggest that host defense by means of antimicrobial peptides might be more general than ever was assumed initially.
Antimicrobial peptides are able to kill a wide variety of gram-positive and gram-negative bacteria. At least three sequential events are required for target cell lysis: membrane binding; permeabilization; and finally damaging of DNA. It is believed that after binding to the cell membrane, the antimicrobial peptides form voltage-dependent channels in the lipid bilayers of the cell membrane. The amphiphatic nature of antimicrobial peptides makes them soluble in aqueous media and promotes their ability to insert in membranes. The net positive charge on antimicrobial peptides favors interactions with negatively charged lipid head groups, and provides an initial driving force for insertion of an antimicrobial peptide into a membrane. Moreover, this mechanism of action is one which bacteria have difficulty evading by developing resistance.
All documents listed in Table 1 hereinabove are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and claims set forth below, many of the devices and methods disclosed in the documents of Table 1 may be modified advantageously by using the teachings of the present invention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to preventing infections associated with implantable medical devices. Those problems include the continued prevalence of infections associated with medical devices, and the ineffectiveness of traditional antibiotics to prevent infection by resistant strains of microorganisms. Various embodiments of the present invention have the object of solving at least one of the foregoing problems.
In comparison with known medical devices, various embodiments of the present invention provide one or more of the following advantages: (a) inhibiting the growth of pathogenic microorganisms by exposure of the microorganisms to antimicrobial peptides; (b) providing a polynucleotide encoding an antimicrobial peptide to a cell present in a patient such that the cell expresses the antimicrobial peptide; (c) providing a cell that expresses an antimicrobial peptide; and (d) making an antimicrobial peptide available at the site of implantation of a medical device and thereby decreasing the likelihood of a medical device associated infection.
Some embodiments of the invention include one or more of the following features: (a) a carrier having a surface that includes a polymer and a polynucleotide associated with at least a portion of the polymer, where the polynucleotide is not present in a cell; and (b) a carrier having a surface that includes a polymer and a cell associated with at least a portion of the polymer, where the cell expresses an antimicrobial peptide.
Definitions
The terms xe2x80x9cmedical device,xe2x80x9d xe2x80x9ccarrier,xe2x80x9d and xe2x80x9cimplantable pulse generatorxe2x80x9d are described in greater detail herein.
As used herein, the term xe2x80x9cporous polymerxe2x80x9d refers to a polymer that has pores distributed throughout, and is capable of absorbing liquids.
As used herein, the term xe2x80x9cpolynucleotidexe2x80x9d refers to a polymeric form of nucleotides of any length, either ribonucleotides or deoxynucleotides, and includes both double- and single-stranded DNA and RNA. A polynucleotide may include nucleotide sequences having different functions, including for instance coding sequences, and non-coding sequences such as regulatory sequences. A polynucleotide can be obtained directly from a natural source, or can be prepared with the aid of recombinant, enzymatic, or chemical techniques. A polynucleotide can be linear or circular in topology. An xe2x80x9cintroduced polynucleotidexe2x80x9d is a polynucleotide that has been introduced to a cell, for instance by ex vivo gene transfer. A polynucleotide can be, for example, a portion of a vector, such as an expression vector, or a fragment.
The phrase xe2x80x9cnot present in a cellxe2x80x9d means the polynucleotide is not present in a eukaryotic or a prokaryotic cell, and is not present in a viral particle.
As used herein, the phrase xe2x80x9cassociated withxe2x80x9d in the context of polynucleotides or cells refers to how they are combined with a carrier polymer. The polynucleotides or cells can be, for instance, incorporated into a polymeric coating or film on the carrier, coated on top of a polymeric coating or film on the carrier, or present under a polymeric coating or film on the carrier. The polynucleotides or cells can also be incorporated into microscopic containment vehicles which are incorporated into a polymeric coating or film on the carrier, coated on top of a polymeric coating or film on the carrier, or present under a polymeric coating or film on the carrier.
As used herein, the term xe2x80x9cfilmxe2x80x9d refers to a sheet material.
As used herein, the phrase xe2x80x9cnatural porous polymerxe2x80x9d refers to a polymer that is present in or produced by nature, i.e., it is not artificial or man-made.
As used herein, the phrase xe2x80x9csynthetic porous polymerxe2x80x9d refers to a polymer that is artificial or man-made, i.e., it is not present in or produced by nature.
xe2x80x9cCoding regionxe2x80x9d and xe2x80x9ccoding sequencexe2x80x9d are used interchangeably and refer to a nucleotide region that encodes a polypeptide and, when placed under the control of appropriate regulatory sequences expresses the encoded polypeptide. The boundaries of a coding region are generally determined by a translation start codon at its 5xe2x80x2 end and a translation stop codon at its 3xe2x80x2 end. A regulatory sequence is a nucleotide sequence that regulates expression of a coding region to which it is operably linked. Nonlimiting examples of regulatory sequences include promoters, transcription initiation sites, translation start sites, translation stop sites, and terminators. xe2x80x9cOperably linkedxe2x80x9d refers to a juxtaposition wherein the components so described are in a relationship permitting them to function in their intended manner. A regulatory sequence is xe2x80x9coperably linkedxe2x80x9d to a coding region when it is joined in such a way that expression of the coding region is achieved under conditions compatible with the regulatory sequence.
xe2x80x9cPeptidexe2x80x9d and xe2x80x9cpolypeptidexe2x80x9d are used interchangeably herein to refer to a polymer of amino acids and does not refer to a specific length of a polymer of amino acids. Thus, for example, the terms oligopeptide, protein, and enzyme are included within the definition of peptide. This term also includes post-expression modifications of the peptide, for example, glycosylations, acetylations, phosphorylations, and the like. The term xe2x80x9cantimicrobial peptidexe2x80x9d is described in detail herein.
The term xe2x80x9ccondensedxe2x80x9d as used herein describes a polynucleotide that has been compacted to isolated spheres or toroids so that the interaction of the DNA with the solvent is minimal.
As used herein, the phrase xe2x80x9clinked to a receptor ligandxe2x80x9d refers to attachment of a receptor ligand to the surface of an encapsulated or condensed polynucleotide. The attachment can be by a covalent bond, hydrogen bonding, or Van der Waals forces.
Unless otherwise specified, xe2x80x9ca,xe2x80x9d xe2x80x9can,xe2x80x9d xe2x80x9cthe,xe2x80x9d and xe2x80x9cat least onexe2x80x9d are used interchangeably throughout the specification and mean one or more than one.